Cardiac pacemakers and other such implantable medical devices (e.g., cochlear implants, defibrillators, neurostimulators, active drug pumps, etc.) typically comprise a hermetically sealed container and a feedthrough assembly having one or more feedthrough terminals (e.g., niobium pins) that provide conductive paths from the interior of the container (e.g., from an anode lead embedded in an internal anode) to one or more lead wires exterior to the device. In the case of a cardiac pacemaker, these lead wires conduct pacing pulses to cardiac tissue and/or detect cardiac rhythms. In general, such feedthrough assemblies comprise a ferrule that secures the assembly relative to the container and an insulating structure (e.g., a glass or ceramic body) that insulates the terminal pin or pins from the ferrule. The feedthrough assembly may be hermetically sealed to prevent body fluids from seeping into the device.
To reduce the effects of stray electromagnetic interference (EMI) signals that may be collected by lead wires coupled to the feedthrough terminal pins, it is known to attach a discoidal capacitor to a feedthrough assembly (a discrete discoidal capacitor for a unipolar feedthrough assembly or a monolithic discoidal capacitor for a multipolar feedthrough assembly). The attached capacitor serves as an EMI filter that permits passage of relatively low frequency electrical signals along the terminal pins while shunting undesired high frequency interference signals to the container. Typically, the attachment of such a capacitor includes the thermal curing of one or more non-conductive epoxy preforms to physically couple the capacitor to a feedthrough assembly. To begin the attachment process, a ring-shaped epoxy preform is threaded over each terminal pin and positioned within a cavity provided along an exterior surface of the feedthrough assembly's ferrule. Next, the capacitor is slipped over the terminal pins and partially inserted into the ferrule's cavity such that the epoxy preforms are sandwiched between the underside of the capacitor and an upper surface of the ferrule. The feedthrough assembly is then placed within a curing oven and heated to a predetermined temperature (e.g., approximately 175 degrees Celsius) to melt the preforms and thereby secure the capacitor in relation to feedthrough assembly and the terminal pins. The feedthrough assembly is then withdrawn from the oven and a conductive material (e.g., epoxy, polyimide, solder, etc.) is dispensed into annular cavities provided between the terminal pins and the terminal pin apertures to electrically couple the feedthrough terminal pins to the inner electrode plates. The entire device may then be centrifuged to remove any voids present in the conductive material, and a second curing step may be performed. Lastly, a non-conductive top coat (e.g., epoxy, polyimide, etc.) may be applied to the upper surface of the capacitor to decrease the likelihood of high-voltage breakdown.
Although feedthrough filter capacitor assemblies of the type described above perform satisfactorily, the installation of such filter capacitor assemblies is relatively complex and time-consuming. For example, if satisfactory seals between the feedthrough pins and the interior annular surfaces of the ferrule are not formed during the thermal curing of the epoxy preforms, the conductive material may travel during centrifuging. Additionally, if the capacitors move in relation to the pins during the curing of the epoxy preforms, a loss of concentricity between the capacitor and the pins may result. Furthermore, the non-conductive epoxy preforms may wick into the annular cavities during curing and thus possibly interfere with the electrical interaction between the terminal pins and the inner electrode plates.
Considering the above, it should be appreciated that it would be desirable to provide a filtered feedthrough assembly utilizing an improved capacitor attachment technique. Additionally, it should be appreciated that it would be desirable to provide a more efficient method of manufacturing filtered feedthrough assemblies that produces reliable, high quality electrical connections. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.